Temperature seasonality in the early middle Eocene North Atlantic region: Evidence from stable isotope profiles of marine gastropod shells

Temperature seasonality, the difference between summer and winter temperatu re, is an important component of the climate, Knowledge about seasonality d uring periods of extreme warmth in Earth history may help us to better unde rstand climate dynamics during global warming. We have established intrashe ll stable isotope profiles of shallow-water gastropods from the warm early middle Eocene Epoch in order to determine the seasonality of coastal sea su rface temperature (SST), Oxygen isotope profiles of shells from Texas and M ississippi suggest a seasonality of 8-9 degrees C along the early middle Eo cene U.S. Gulf Coast, with a winter temperature of 19 degrees C and a summe r temperature of 27-28 degrees C, Relative to the present temperatures In t he area, the Eocene summer temperature was similar, whereas the winter temp erature was 7-8 degrees C higher. A probable reason is a smaller impact tha n today by cold continental air from the north because of higher continenta l winter temperatures, Isotope profiles of shells from southern England ind icate early middle Eocene seasonality similar to present day,about 10-12 de grees C, whereas the mean temperature was 8-10 degrees C higher in Eocene t ime. These data confirm previous temperature estimates of the early middle Eocene Epoch in France, Using the gastropod delta(18)O temperatures in this and previous studies, we have established preliminary maps of winter and s ummer SSTs of the Eocene North Atlantic The latitudinal temperature gradien t in the summer seems to have been insignificant, whereas in the winter the gradient was prominent but significantly less steep than today, Increased oceanic heat transport has been suggested as a primary mechanism for the ea rly Cenozoic warm climate, Strong oceanic heat transport significantly redu ces the seasonality of coastal SST and surface air temperature. As the seas onality in western Europe seems to have been similar to that today, oceanic heat transport was probably not essentially higher than at present. Atmosp heric properties and feedback effects were likely of more importance for ma intaining the reduced latitudinal temperature gradient.